1. Field of the Invention
The present invention relates to an optical wavelength demultiplexing detector for fluorescence analysis and a fluorescence detection system having the same.
2. Description of the Related Art
To detect a trace quantity of material being present in a minute region such as a micro-well, a micro-chemical chip, a micro-capillary, or the like, optical measurement methods such as thermal lens spectrophotometry and fluorescence spectrometry are commonly used.
In the fluorescence spectrometry, by irradiating light with a predetermined wavelength onto a sample, and measuring a fluorescence emitted by the sample, a concentration of a material to be measured included in the sample is measured. As a system for such fluorescence detection, a fluorescence detection system with an arrangement shown in FIG. 6 has been proposed (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2005-30830).
In this fluorescence detection system, light with a predetermined wavelength (an excitation light) emitted from a light source 91 is transmitted to an optical demultiplexer 92 via an optical fiber 95 (a first optical transmission path), then transmitted from the optical demultiplexer 92 to an optical fiber 96 (a second optical transmission path), and after that, outputted from a probe 94 mounted at a distal end of the optical fiber 96 toward a sample 99. A fluorescence emitted by the sample as a result of the irradiation of the excitation light is received by the probe 94, transmitted to the optical demultiplexer 92 via the optical fiber 96, then transmitted to a detector 93 through an optical fiber 97 (a third optical transmission path), and converted into an electric signal by a detector 93.
FIG. 7 schematically shows an arrangement of the optical demultiplexer used in the fluorescence detection system in FIG. 6. The optical demultiplexer 92 is arranged such that two lenses 82 and 83 disposed with an optical demultiplexing filter 81 interposed therebetween, a first capillary 84 that holds the optical fibers 95 and 96, and is disposed on the lens 82 side, and a second capillary 85 that holds the optical fiber 97 and is disposed on the lens 83 side are held by a cylindrical holding member 86.
The excitation light generated by the light source 91 is outputted from the optical fiber 95 to the lens 82, passes through the lens 82 to be reflected by the optical demultiplexing filter 81, and passes through the lens 82 to fall upon the optical fiber 96. Also, the fluorescence generated by the sample 99 propagates through the optical fiber 96, is outputted to the lens 82, passes through the lens 82 and the optical demultiplexing filter 81 to fall upon the lens 83, passes through the lens 83 to fall upon the optical fiber 97, propagates through the optical fiber 97, and is guided to the detector 93.
However, an optical fiber has a minimum winding radius (bending minimum curvature), and cannot be bent to the value or less, and hence when a number of optical fibers are used, they occupy a wide space in the apparatus. It is thus preferred that the number of optical fibers to be used is minimized. Moreover, because the apparatus must be handled in such a manner as not to break optical fibers, it is preferred that the number of optical fibers to be used is minimized so as to make the apparatus easier to handle. Further, the optical demultiplexer 92 arranged as shown in FIG. 7 has a number of components and takes a lot of time to assemble, and hence its production cost is high.